Spring assemblies or spring interiors such as those used in inner spring mattresses are usually made of rectangular arrays of individually coiled springs linked together with transverse coils of lacing wire. These assemblies are presently made on automated machinery that includes one or more coil forming machines or coilers, a coil collecting conveyor, a coil row transfer device and a coil row assembler. The coil machines produce individual coils and place them on the conveyor. The conveyor collects and then conveys rows of coils, one row at a time, to the row transfer machine. The row transfer machine transfers the rows of coils, one row at a time, transversely into an assembly machine which laces the rows together to form a rectangular array that becomes the spring interior assembly of an inner spring mattress. Systems for making these assemblies are described in U.S. Pat. Nos. 3,386,561; 3,774,652; 4,111,241; 4,413,659; 4,705,079; 5,579,810 and 5,934,339, which are all hereby expressly incorporated herein by reference.
In the automatic production of these spring assemblies, manufacture of rectangular arrays is the easiest, and the spring assembly making machinery is typically configured to assemble spring interiors in these rectangular arrays. Where softer mattresses are desired to be made, the convenient way of doing so is to use softer springs in the arrays.
Before the automated manufacture of spring assemblies became dominant, when spring interiors were assembled by hand, relatively soft spring units were often made by hand lacing coils with spaces between adjacent coils of a row so that few coils per unit area of mattress were present. Early spring assemblies made of low density arrays of unknotted coils are described, for example, in the 1934 Swiss Patent No. 165465 to Buron and in the 1935 French Patent No. 793.155 to Simmons. The absence of knos to secure the ends of the wire of the coils presents few problems when units are assembled by hand. When machines became common for assembling spring interiors, unknotted coils were found to be dimensionally unstable and difficult to handle with automated gripper devices, and arrangements of coils at widely spaced intervals were not compatible with the machinery.
Therefore, there is a need for a method and machinery for the automated assembly of spring interiors for mattresses that have low density arrays of individual coil springs, particularly coil springs without knotted wire ends.